The design of golf clubs and particularly that of putters is typically viewed as a pursuit of an aesthetically pleasing club that promotes a golfer's confidence in his or her stroke. As such, many putters have been designed irrespective of the mechanics inherent in the putting swing. Furthermore, many putters lack a design that accounts for an individual golfer's characteristics and characteristic playing style (i.e., stance, grip, etc.).
The lack of attention to technical details in many putter designs results in clubs that are not aimed or balanced properly. Such technical considerations, for example, include heel and toe weight distribution, location of the putter head's center of gravity or “sweet spot,” putter length, shaft flexibility, grip, head weight and total club weight, loft, and lie. Because the USGA Rules of Golf permit significant latitude in the design of putters, i.e., the shaft, neck or socket of a putter may be fixed at any point in the head, many putter designs are possible. And, because significant deviation in the intended path of a putt can be experienced for even slightly off-center hits, careful attention to these design factors can result in a putter that is more likely to perform well in use. Moreover, an adjustable length putter design may permit the variation of one or more of the aforementioned design considerations to more closely suit the needs of a given user.
What follows is an excerpt from a publication of the United States Golf Association entitled “A Guide to the Rules on Clubs and Balls”, and in particular an excerpt regarding the rules for the adjustability of clubs:
“Adjustability Appendix II, 1b states that:                Woods and irons shall not be designed to be adjustable except for weight. Putters may be designed to be adjustable for weight and some other forms of adjustability are also permitted. All methods of adjustment permitted by the Rules require that:        (i) the adjustment cannot be readily made;        (ii) all adjustable parts are firmly fixed and there is no reasonable likelihood of them working loose during a round; and        (iii) all configurations of adjustment conform with the Rules.        The disqualification penalty for purposely changing the playing characteristics of a club during a stipulated round (Rule 4-2a) applies to all clubs including a putter.        
(i) General                In order to preserve the integrity of Rule 4-2 (Playing Characteristics Changed), this rule clearly states that it must not be too easy for a player to make adjustments during the course of a stipulated round. This is interpreted to mean that adjustments must require the use of a special tool, such as an Allen key or a Phillips screwdriver. It must not be possible to make the adjustments during a round.        
(II) Adjustability for Weight                All clubs may be designed to be adjustable for weight, provided the adjustment mechanism conforms to the conditions described previously and in Appendix II, 1b of the Rules. Examples of what would and would not be permitted are illustrated below. [see FIG. 1 b]        As already noted in Design of Clubs, Section 1a, with respect to adjustments for weight, the only exception to the conditions described in (i) above is the addition or removal of lead tape. This is a practice which pre-dates the introduction of the adjustability rules and is permitted on ‘traditional’ grounds. Of course, the addition or removal of lead tape during a round is not permitted (see Rule 4-2a and Decision 4-2/0.5 in “Decisions on the Rules of Golf”).        
(III) Other Kinds of Adjustability                Only putters may be designed to be adjustable in ways other than weight. For example, a putter may be designed to be adjustable for lie and length. Again, these adjustments must require the use of a special tool, not just the fingers or a coin, etc. If, as is often the case, a screw is used to fix the mechanism, the putter must, for all practicable purposes, be unusable without the screw being in place and tightly fixed.        When assessing the conformity of an adjustable putter, it is important to remember the third condition listed in Appendix II, 1b, and to ensure that the putter cannot be adjusted into a position which does not conform to the Rules. For example, a putter which is adjustable for lie must not be adjustable into a position where the shaft diverges from the vertical by less than ten degrees (see Appendix II, 1d and Design of Clubs, Section 1d), or any other position which would render the club non-conforming.”        
Various adjustable club constructions are known. For example, U.S. Pat. No. 2,305,270 to Nilson discloses a golf club with a hosel that has an extension on which the head is slideably and pivotally mounted. The extension is embedded in a shallow depression in the back of the head and runs substantially the entire length of the head. The head further includes lugs with inner serrated portions, and when a desired angle has been selected for the face, serrated portions on the extension are engaged with the lugs to lock the position.
U.S. Pat. No. 6,780,120 to Murray teaches an extendable shaft of two pieces. The upper shaft has a captured screw member (a bolt) that is screwed into an operative receipt (a nut) in the lower shaft. This invention allows the shaft to be extended but not adjusted.
U.S. Pat. No. 6,896,626 to Drossos also teaches an extendable shaft of two pieces. A male non-circular annular flange is mounted to one section of the shaft, a female non-circular annual flange relief is mounted to the other section of the shaft, and a locking means couple the two sections to form the shaft. This invention also allows the shaft to be extended but not adjusted.
In addition, U.S. Pat. No. 7,018,302 to Jacoby teaches an extension shaft having a protruding threaded end which engages with a threaded aperture in a coupling device.
U.S. Pat. No. 7,850,540 to Sander et al. teaches a golf club having a shaft, a collet, and a club head having an interior chamber configured to receive the collet. This invention does not teach an adjustable shaft or an extendible shaft.
U.S. Pat. Appl. No. 2003/0050131 to Grace teaches an extendable shaft of two pieces. The shaft extensions are of predetermined length and are not adjustable.
U.S. Pat. Appl. No. 2003/0148819 to Lindner teaches an elongated shaft having a housing into which is inserted a predetermined weight. This invention allows the shaft to be extended and weighted but not adjusted.
U.S. Pat. Appl. No. 2005/0143186 to Blattner et al. teaches a shaft extension that is attached by means of a reverse-thread connection. This invention allows the shaft to be extended but not adjusted.
Despite these developments, there exists a need for an improved golf club construction. In particular, there is a need for an improved golf club with adjustable shaft length.